Thank you Patrick, Your email is very important for one reason, we on this forum Should share general inquiries only and not actual or private Information for the full public. I have heard of the 6db rule to In the past, but I think its one of those things, that says Silently we design better than you, we only ship 6db or quieter. When at the lab, I only engage in pleastant conversation, Never in detail on the actual job at hand. I think the same should Go on here, help and assistance is important on here, But getting down to a company and individuals engineering status Or actual numbers may not be to wise. It is good that everyone on here is here for the same purpose. I notice at times conflicting answers to the same question posted. What does that person do? He can only choose one, and he or she May never know which is the correct one. Almost like going to a Dr. then another for 2nd opinion. Interesting subject for sure. Regards Richard,
From: [email protected] [mailto:[email protected]] On Behalf Of Conway, Patrick R (Houston) Sent: Wednesday, June 27, 2007 3:24 PM To: Kunde, Brian; [email protected] Subject: RE: Internal Margins for Emissions Testing Brian- Good luck in your search for the correct balance. As an example of what you are trying to avoid, here is a quick anecdote from my past: At my first job as an EMC engineer our company had a margin requirement of 6 dB. The reason was: "our competitor did it that way". We EMC engineers had many 24 hour work days, and long weekends, as we struggled to meet the margin. The company lost several talented engineers because of the workload. (I stayed around a few more years- not smart enough at that time!) We also lost millions of dollars in revenue because we were late to market on several projects. Turns out that our competitor never really had 6 dB of margin- they just told everyone they did! Ha! Since then I've learned that it makes better business sense to have a reasoned plan, with constant & intelligent real-time review of the plan, than to just pull a number from a hat. Best Regards, Patrick. [email protected] From: Kunde, Brian [mailto:[email protected]] Sent: Wednesday, June 27, 2007 10:15 AM To: Conway, Patrick R (Houston); [email protected] Subject: RE: Internal Margins for Emissions Testing Patrick, Great analyses. For some companies who get passing data on a golden unit then produces that product for less than a year and never audits, then I can see where margin would have little benefit. But our company has products that have been in production for over 25 years (with technical upgrades). We audit every family of product (about 50 families) at least once a year. If we fail the audit, we have to shut down production until a solution is found. It requires additional time and manpower from our department. If we need assistance from Engineering, then they have to pull engineers off of new product development to help. Once a solution is found, then there are Stop-Ship ECNs, prints, process sheets, rework, field upgrades, yada yada yada..... The cost can be high and the delay in shipping can make our customers very unhappy. But, if we originally design our products with a reasonable margin, and we loose some of that margin during an audit (but still passes), we can take our time, investigate, and find out why we lost margin without shutting down production and raising the red flag. Once we find the cause of the reduction in margin, we can put through a standard ECN where the solution can be phased in without expensive rework. I think this scenario is more real than a failing product being caught in the field. In a previous life, I had a buy/sell product audited by SEMKO. It failed emissions by 4db at their OATS but they justified this in their report by stating possible differences in measurements made >from one OATS to another. So they let it go. I think as long as your product isn't blacking out entire neighborhoods or causing planes to drop out of the ski then you most likely will not get in trouble (my opinion only). But, my name is on the DOC and I will not look the other way if I know a product is failing, so margin makes my life a lot easier and whether my company realizes it or not, margin is saving them money and problems. The problem I have, which started this tread, is how to get management and engineering behind the idea of margin. The argument I made above is a good one, but when push comes to shove, margin will be sacrificed over shipping most of the time. I wish the standard had the margin built in somehow, but that doesn't seem practical for everyone. I appreciate the many comments and advice I have received. It has been most helpful. The Other Brian From: Conway, Patrick R (Houston) [mailto:[email protected]] Sent: Tuesday, June 26, 2007 6:01 PM To: Kunde, Brian; [email protected] Subject: RE: Internal Margins for Emissions Testing It seems from Brian's email, and the responses so far, that test margin is a presumption. Why? Why is it presumed that we need any margin at all? If we can answer that question, then the "amount" of margin needed should follow easily. Here are some basic questions we compliance engineers should ask of our companies. What problem do we solve by having margin during testing? (If there is not a well defined problem, then we should stop right here!) Does that problem get solved "better" by adding more margin? (can you show that doubling your margin improves your problem solution by 2x ? ) Are the percentages, probabilities and uncertainties associated with that margin truly defensible? (defensible in a mathematical and manufacturing sense, not a legal sense) If a problem occurs in the field, does the required margin shown in the test report gain you any advantage in discussions with the customer or auditing body? (so, you did one test and passed. Then you manufacture 10 million a month. What does that margin buy you?) IMHO - these are the basic questions a company should answer before committing to any compliance plan. Best Regards, Patrick. [email protected] From: [email protected] [mailto:[email protected]] On Behalf Of Kunde, Brian Sent: Tuesday, June 26, 2007 12:13 PM To: [email protected] Subject: Internal Margins for Emissions Testing Good people of the EMC-PSTC Group, I once again seek out your wisdom. We are an internal corporate EMC/Safety test lab. Most of the EMC testing we do are either Pass or Fail. But with Emissions testing (Radiated and Conducted) we want to pass with enough margin to insure our production stays compliant. The amount of margin that is accepted is always in debated between our department and engineering. I'm sure many of you have had similar problems. My question is how do you convey the desired margin on your test reports or other documents so the standard limits and internal limits (with margin) are properly documented and hopefully understood. Do you show two limit lines on your graphs an/or multiple limits and margins in your data tables? How does your Measurement Uncertainty factor into your data and how it is reported/documented? How are emissions requirements conveyed to engineering so they know what they are to design to (Limit plus some margin)? I know this seems like a newbie questions, but I am hoping that some of you have found cleaver new ways of dealing with this problem which has been around since the beginning of time. Thanks in advance for any and all replies, The Other Brian. LECO Corporation Notice: This communication may contain confidential information intended for the named recipient(s) only. If you received this by mistake, please destroy it and notify us of the error. Thank you. - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc LECO Corporation Notice: This communication may contain confidential information intended for the named recipient(s) only. 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